This sentence needs someone's name before "gwiha" to make perfect sense and "gwiha" has to be replaced with "님(nim)" or "씨(ssi)" because the term "gwiha" is usually added to the end of a formal letter before reciever's or company name.:) So, it can be "Pascal 님, 오신 것을 환영합니다" meaning "Dear Pascal, welcome to visit us(=our country)" or "Dear Pascal, welcome to join us(in a chatroom, meeting or stuff like that)" \^o^/

It means, welcome to your visit.